(1) Field of the Invention
This invention relates to a method of and apparatus for controlling reaping levels by utilizing a noncontact distance sensor. More particularly, the invention relates to a method of and apparatus for controlling reaping levels comprising the steps of deriving an average level from a certain number of level measurement data based on outputs of a noncontact distance sensor worked in fixed cycles, the data being memorized in order to measurement, deriving a difference between the average level and a predetermined target level for said measurement data, and providing a drive pulse signal having a length corresponding to the amount of the difference therebetween, which signal drives an actuator for vertically moving a reaper.
(2) Description of the Prior Art
Generally the distance sensor used to automatically control reaping levels comprises a contact type distance sensor utilizing an actuator adapted to contact the earth or a noncontact type distance sensor such as a ultrasonic wave distance sensor having an ultrasonic wave transmitter and an ultrasonic wave receiver. The contact type distance sensor, however, has a disadvantage that the actuator could be damaged when, for example, the machine body suddenly inclines by a great degree. Therefore, from the point of view of reliability, stability and so on the noncontact type distance sensor such as the ultrasonic wave sensor is increasingly favored.
In a known method of controlling reaping levels utilizing the noncontact distance sensor, levels measured in a certain cycle are compared with a predetermined reference level and a reaping implement is moved up and down at a certain speed according to the difference therebetween. However, where there are footprints or stubbles, for example, the use of measurement data per se for comparison with the reference level causes an abrupt rise or fall of the reaping implement which results in instability in the vicinity of a target level. In order to eliminate such a disadvantage the reaping implement may be vertically controlled on the basis of an average of data derived from a series of measurements.
However, if a large number of data is averaged, there occurs a great difference between actual distances and an averaged distance. This is liable to cause overshooting to occur when the reaping implement is rapidly moved in a vertical direction. If a small number of data is averaged, minor irregularities on the earth tend to unduly influence detrimentally reaper stability in the vicinity of the target level.
Furthermore, the noncontact distance sensor such as the ultrasonic wave sensor, by nature, becomes incapable of accurate measurement even if the sensor per se is in good working order, as a result of an echo attentuation which occurs when, for example, an ultrasonic wave is transmitted to soft straw lying on the earth or when a divider cuts into a stubble and the wave is transmitted into the stubble. Consequently, wrong data cause a gross error in the average level derived from the measurement data, making it impossible for the reaping implement to follow the target level.